High speed laser scan module with folded beam path

ABSTRACT

A retroreflective optical scan module, for example for in a bar code reader including a light source mounted on the base of the module and at least one fold mirror for reflecting and redirecting the scanning light beam along an optical path which is parallel to the base and over at least a portion of the top side surface of the module, so that the scanning beam is longer than the length of the side of the module which the scanning beam passes over enroute to the target.

RELATED APPLICATIONS

[0001] The present application is related to U.S. application Ser. No.09/223,482 filed Dec. 30, 1998, which was a continuation-in-part of Ser.No. 09/048,418 filed Mar. 26, 1998, now U.S. Pat. No. 6,114,712, bothapplications which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The field of the invention relates to electro-optical readers orscanning systems, such as bar code symbol readers, and more particularlyto the optical path design in a scanning module for use in applicationsrequiring a relatively long single line scan line near the reader in acompact bar code reader.

[0004] 2. Description of the Related Art

[0005] Electro-optical readers, such as bar code symbol readers, are nowvery common. Typically, a bar code symbol comprises one or more rows oflight and dark regions, typically in the form of rectangle. The widthsof the dark regions, i.e., the bars and/or the widths of the lightregions, i.e., the spaces, between the bars encode information in thesymbol.

[0006] A bar code symbol reader illuminates the symbol and senses lightreflected from the regions of differing light reflectivity to detect therelative widths and spacings of the regions and derive the encodedinformation. Bar code reading type data input systems improve theefficiency and accuracy of data input for a wide variety ofapplications. The ease of data input in such systems facilitates morefrequent and detailed data input, for example to provide efficientinventories, tracking of work in progress, etc. To achieve theseadvantages, however, users or employees must be willing to consistentlyuse the readers. The readers therefore must be easy and convenient tooperate.

[0007] A variety of scanning systems are known. One particularlyadvantageous type of reader is an optical scanner which scans a beam oflight, such as a laser beam, across the symbols. Laser scanner systemsand components of the type exemplified by U.S. Pat. Nos. 4,387,297 and4,760,248, which are owned by the assignee of the instant invention andare incorporated by reference herein, have generally been designed toread indicia having parts of different light reflectivity, i.e., barcode symbols, particularly of the Universal Product Code (UPC) type, ata certain working range or reading distance from a hand-held orstationary scanner.

[0008] In the laser beam scanning systems known in the art, a singlelaser light beam is directed by a lens or other optical components alongthe light path toward a target that includes a bar code symbol on thesurface. The moving-beam scanner operates by repetitively scanning thelight beam in a line or series of lines across the symbol by means ofmotion or a scanning component, such as the light source itself or amirror disposed in the path of the light beam. The scanning componentmay either sweep the beam spot across the symbol and trace a scan lineacross the pattern of the symbol, or scan the field of view of thescanner, or do both. The laser beam may be moved by optical oropto-mechanical means to produce a scanning light beam. Such action maybe performed be either deflecting the beam (such as by a moving opticalelement, such as a mirror) or moving the light source itself. U.S. Pat.No. 5,486,944 describes a scanning module in which a mirror is mountedon a flex element for reciprocal oscillation by electromagneticactuation. U.S. Pat. No. 5,144,120 to Krichever et al., describes laser,optical and sensor components mounted on a drive for repetitivereciprocating motion either about an axis or in plane to effect scanningof the laser beam.

[0009] Another type of bar code scanner employs electronic means forcausing the light beam to be deflected and thereby scan a bar codesymbol, rather than using a mechanical motion to move or deflect thebeam. For example, a linear array of closely spaced light sourcesactivated one at a time in a regular sequence may be transmitted to thebar code symbol to simulate a scanned beam for a single source. Insteadof a single linear array of light sources, a multiple-line array mayalso be employed, producing multiple scan lines. Such type of bar codereader is disclosed in U.S. Pat. No. 5,258,605 to Metlitsky et al.

[0010] Bar code reading systems also include a sensor or photodetectorwhich detects light reflected or scattered from the symbol. Thephotodetector or sensor is positioned in the scanner in an optical pathso that it has a field of view which ensures the capture of a portion ofthe light which is reflected or scattered off the symbol, detected, andconverted into an electrical signal. Different photodiode arrangementsare described in U.S. Pat. Nos. 5,635,700; 5,682,029; and 6,213,399.

[0011] In retroreflective light collection, a single optical componente.g., a reciprocally oscillatory mirror, such as described in Kricheveret al. U.S. Pat. No. 4,816,661 or Shepard et al. U.S. Pat. No.4,409,470, both herein incorporated by reference, and U.S. Pat. No.6,114,712, filed Oct. 9, 1996, scans the beam across a target surfaceand directs the collected light to a detector. The mirror surfaceusually is relatively large to receive as much incoming light as ispossible, only a small detector is required since the mirror can focusthe light onto a small detector surface, which increases signal-to-noiseratio.

[0012] Of course, small scan elements are preferable because of thereduced energy consumption and increased frequency response. When thescan element becomes sufficiently small, however, the area of thescanning mirror can no longer be used as the aperture for the receivedlight. One solution is to use a staring detection system (anon-retroreflective system) which receives a light signal from theentire field which the scanned laser spot covers.

[0013] In non-retroreflective light collection, the reflected laserlight is not collected by the same optical component used for scanning.Instead, the detector is independent of the scanning beam, and istypically constructed to have a large field of view so that thereflected laser light traces across the surface of the detector. Becausethe scanning optical component, such as a rotating mirror, need onlyhandle the outgoing light beam, it can be made much smaller. On theother hand, the detector must be relatively large in order to receivethe incoming light beam from all locations in the scanned field.

[0014] Electronic circuitry and software decode the electrical signalinto a digital representation of the data represented by the symbol thathas been scanned. For example, the analog electrical signal generated bythe photodetector may be converted by a digitizer into a pulse widthmodulated digitized signal, with the widths corresponding to thephysical widths of the bars and spaces. Alternatively, the analogelectrical signal may be processed directly by a software decoder. See,for example, U.S. Pat. No. 5,504,318.

[0015] The decoding process of bar code reading systems usually works inthe following way. The analog signal from the sensor or photodetectormay initially be filtered and processed by circuitry and/or software toremove noise, adjust the dynamic range, or compensate for signalnon-uniformities. Samples may then be taken of the analog signal, andapplied to an analog-to-digital converter to convert the samples todigital data. See, for example, U.S. Pat. No. 6,170,749, which is herbyincorporated by reference. Alternatively, analog circuitry may be usedto digitize the shape of the signal.

[0016] A variety of mirror and motor configurations can be used to movethe beam in a desired scanning pattern. A scanner which produces anelongated scan line is described in U.S. Pat. No. 5,621,203. U.S. Pat.No. 4,251,798 discloses a rotating polygon having a planar mirror ateach side, each mirror tracing a scan line across the symbol. U.S. Pat.Nos. 4,387,297 and 4,409,470 both employ a planar mirror which isrepetitively and reciprocally driven in alternate circumferentialdirections about a drive shaft on which the mirror is mounted. U.S. Pat.No. 4,816,660 discloses a multi-mirror construction composed of agenerally concave mirror portion and a generally planar mirror portion.The multi-mirror construction is repetitively reciprocally driven inalternative circumferential directions about a drive shaft on which themulti-mirror construction is mounted. U.S. Pat. No. 6,247,647 describesan arrangement for providing either a multiple line, or single line,scan pattern by means of a controller. All of the above-mentioned USpatents are incorporated herein by reference.

[0017] In electro-optical scanners of the type discussed above, theimplementation of the laser source, the optics the mirror structure, thedrive to oscillate the mirror structure, the photodetector, and theassociated signal processing and decoding circuitry as components alladd size and weight to the scanner. In applications involving protracteduse, a large, heavy scanner can produce user fatigue. When use of thescanner produces fatigue or is in some other way inconvenient, the useris reluctant to operate the scanner. Any reluctance to consistently usethe scanner defeats the data gathering purposes for which such bar codesystems are intended. Also, a need exists for an interchangeable compactslim and module to fit into small compact devices, such as notebooks,portable digital assistants, pagers, cell phones, and other pocketappliances.

[0018] Thus, an ongoing objective of bar code reader development is tominiaturize the reader as much as possible, and a need still exists tofurther reduce the size and weight of the scan module and to provide arelatively thin or flat scan module, so that the single scan line can beelongated close to the reader. The mass of the moving components shouldbe as low as possible to minimize the power required to produce thescanning movement.

[0019] It is also desirable to modularize the scan engine so that aparticular module can be used in a variety of different appliances. Aneed exists, to develop a particularly compact, lightweight module whichcontains all the necessary scanner components for such applications.

SUMMARY OF THE INVENTION

[0020] Objects of the Invention

[0021] It is an object of the present invention to provide a module foruse in a bar code reader capable of emitting an elongated scan lineclose to the module.

[0022] It is another object of the invention to provide a module thatemits a scan line over and parallel to the top surface of the module.

[0023] It is a further object of the present invention to provide anon-retroreflective scan module with multiple photodectectors.

[0024] It is still further object of the present invention to providecollection optic in a scan module with adjusts the optical power as afunction of position on the scan line.

[0025] A related object is to provide a non-retroreflectiveelectro-optical scanning module which is both thinner, smaller andlighter in weight then using discrete optical components, whileproviding a collector area of at least 20 mm².

[0026] It is yet a further object to produce a module having astep-shaped form factor which may be manufactured with a print circuitboard forming the base of the module.

[0027] Additional objects, advantages and novel features of the presentinvention will become apparent o those skilled in the art from thisdisclosure, including the following detailed description, as well as bypractice of the invention. While the invention is described below withreference to preferred embodiments, it should be understood that theinvention is not limited thereto. Those of ordinary skill in the arthaving access to the teachings herein will recognize additionalapplications, modifications and embodiments in other fields, which arewithin the scope of the invention as disclosed and claimed herein andwith respect to which invention could be of significant utility.

[0028] Features of the Invention

[0029] Briefly, and in general terms, the present invention provides ascan module for use in bar code reading systems for reading indiciahaving portions of different light reflectivity and located on a targetat a distance from the scan module, including a generally rectangularmodule including a support having a generally planar base and planarperipheral sides orthogonal thereto: a laser light source mounted on thesupport for producing a light beam; a scan mirror mounted on the supportin spaced relationship to the light source and positioned so that thelight beam from the light source is directed by the scan mirror along afirst optical path to a fold mirror mounted on the support which directsthe light beam along a second optical path exterior to the scan modulein the direction of the target. There are further provided a drivemoving the scan mirror so that the light beam is moved in a scanningpattern substantially parallel to the peripheral sides of the supportand across the indicia to be read; and at least one sensor mounted onthe support for directly receiving reflected light from the target andconverting the reflected light in to an electrical signal.

[0030] According to another aspect of the invention there is provided anoptical scan module having mounted thereon a light source for emitting alight beam; and a scanning assembly for receiving said light beam andfor generating therefrom a scanning beam directed to the bar code symbolto be scanned so that the emitted scanning beam is longer than the sideof the module which the scanning beam passes over enroute to the target.

[0031] According to yet another aspect the invention there is provided asmall-size optical scan module in the form factor of a substantiallyrectangular, step-shaped, parallelepiped module having dimensionsapproximately 42 mm×24 mm×11 mm. In the first embodiment, on one of thelarger sides (i.e. preferably a peripheral side 42 mm×24 mm there ismounted thereon a light source for emitting a light beam, a scanningassembly for receiving said light beam and for generating therefrom ascanning beam directed to an indicia to be read, at least onephotodtector and collection optics arranged to received reflected lightfrom the symbol and to direct it to said detector.

[0032] The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 is a perspective view of an optical assembly according to afirst preferred embodiment of the invention;

[0034]FIG. 2 is a particularly sectioned perspective view of an opticalassembly according to a second preferred embodiment of the invention;

[0035]FIG. 3 shows a schematic of the use of four discretephotodectectors in the optical assembly according to another embodimentof the invention; and

[0036]FIGS. 4, 5, and 6 are depictions of the operation of a collectionlens in one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] The invention relates to bar code readers of the type generallydescribed in the above identified patents and patent applications forreading bar code symbols. As used in this specification and the claims,the term “bar code symbol” is intended to be broadly construed and tocover not only symbol patterns composed of alternating bars and spaces,but also other graphic patterns, such as dot or matrix array patterns,and, in short, indicia having portions of different light reflectivityor surface characteristics that results in contrasting detected signalcharacteristics that can be used for encoding information and can beread and decoded with the type of apparatus disclosed herein.

[0038] As a preferred embodiment, we describe the implementation of thepresent invention in a laser-scanning, bar code reading module similarto the module illustrated in FIG. 1. The modular device of FIG. 1 isgenerally of the style disclosed in U.S. Pat. No. 5,367,151, issued toDvorkis et al. assigned to Symbol Technologies, Inc. and herebyincorporated by reference, and also similar to the configuration of abar code reader commercially available as part number SE 1000 or SE 1200from Symbol Technologies, Inc. of Holtsville, N.Y. Alternatively, or inaddition, features of U.S. Pat. Nos. 4,387,297, and 4,760,248 issued toSwartz et al., or U.S. Pat. No. 4,409,470 issued to Shepard et al., bothsuch patents assigned to Symbol Technologies, Inc., may be employed inconstructing the bar code reader module of FIG. 1. These U.S. Pat. Nos.4,760,248, 4,387,297 and 4,409,470 are incorporated herein by reference.

[0039] The module 200 shown in FIG. 1 is formed from an integral frameor assembly 201 which is generally a rectangular parallelepiped inshape, having a front wall side 202, side walls 203 and 204, preferablyan open top surface 205 over which a laser beam 206 is scanned along ascanning path 216, and a bottom surface (not shown) enclosed by aprinted circuit board 207 on which electrical components may be mounted.A laser diode assembly 208 is mounted on the frame 201 for producing alight beam 209, which is emitted through aperture 210 in the laser diodeassembly. The light beam 209 is directed to the scanning mirror 211 fromwhich it is reflected and scanned along path 212 to fold mirror 213(only the edge of which is seen) which is mounted on the front wall 202of the assembly. The beam is then reflected from fold mirror 213 alongpath 214 to the fold mirror 215. The beam is then reflected from mirror215 and directed along path 206 over the surface 205 and exteriorly ofthe module 200 in the direction of the target 212.

[0040] Light is scattered or reflected from the symbol to the opticalcollection lenses 217 and 218 behind, which is are photodetectors.

[0041] The Figure also depicts a drive coil 220 and moving mirrorassembly 219 which supports the mirror 211 and moves in response tocurrent changes in the drive coil 220.

[0042] The laser diode 208 may be operated in a continuous “constantpower” mode, pulsed, or modulated with different power levels, dependingon the specific application. It is also known to provide circuitry tomaintain the laser diode at a predetermined output power level using aclosed-loop feedback circuit using a monitor photodiode associated withthe diode.

[0043] The optical subassembly associated with the laser diode 208 mayinclude a focusing lens and/or aperture stop of the following lenstypes, depending on the application: spherically symmetric glass orplastic lenses; aspheric glass or plastic lenses, rotationally symmetricas well as non-rotationally symmetric around the optical axis, such ascylindrical optical elements as well including gradient index lens,Fresnel lens, binary optical lens, or multi-level binary optical lens;lens systems where the lens diameter itself acts as a functionalaperture stop for the system; or holographic optical elements, includingbut not restricted to Fresnel “zone plate” optics.

[0044] Turing next to another embodiment, shown in FIG. 2 from adifferent perspective, the laser beam is directed to an optical element211, such as a planar mirror, which is moved so as to cause the beam tobe deflected into a scanning beam 216 which is directed exteriorly ofthe module 200 towards a target plane. The beam 206 is focused by theoptical subassembly to form a spot on the target plane which moves alongthe scanning path 216 through the bars of the bar code symbol 228 on thetarget plane as the mirror 211.

[0045] The optical element 211 is mounted on an assembly 219 which iscaused to oscillate when alternating current is introduced in the coil220. The oscillation results in a movement of the element 211 through anarc about a pivot axis A.

[0046] The scanning mirror 211 is mounted for oscillation about an axis,this being achieved by virtue of the interaction between a permanentmagnet 221 and a driven electromagnetic coil 220. A suitable drivingsignal is applied to the coil, via the PCB 207 and coil electricalcontacts.

[0047] The scanner motor drive 12 shown in FIG. 1 is exemplary, and maybe replaced with any type of mechanism for effecting a scanning motionof the laser beam in one or two dimensions. For example, the scannermotor drive could comprise any of the configurations disclosed in U.S.Pat. Nos. 5,581,067 and 5,367,151, all of which are incorporated byreference. In this way, the static optics assembly may be used as acomponent in a variety of scanner designs.

[0048] The light reflected from the symbol is received by thephotodetector 224 a, 224 b, 225 a and 225 b which are illustrated asdiscrete devices mounted behind the collection lenses 222.

[0049] The subassembly or device of FIGS. 1 and 2 may be implemented inany type of bar code reader, fixed or portable.

[0050] The photodetector output signal is then passed on to suitableelectronics within the PCB 207 by an electrical coupling 42.

[0051] Although a light masking aperture may be used in front of thephotodetector for increasing the depth of focus of the photodetector,the same effect can be achieved without an aperture by appropriatelyspecifying the area of the photodetector itself.

[0052] In another preferred embodiment, the type of motor drive used tooscillate the scan mirror can be a Mylar leaf spring supporting anunbalanced mirror assembly. The mirror assembly is mounted to a Mylarleaf spring which flexes as the permanent magnet is driven by the ACcoil imparting an oscillating force.

[0053] Yet a further alternative is a “micro machined” mirror assemblyas discussed in U.S. patent application Ser. Nos. 08/506,574 and08/631,364 according to which the mirror is driven back and forthdirectly by a suitable drive motor, preferably of very small dimension.Yet a further alternative is to use a mirror of known rotating polygontype as discussed in the introduction in relation to U.S. Pat. No.4,251,798 according to which the mirror comprises a solid body having aplurality of face angled to one another. As the body rotates the beam isscanned by successive rotating faces of the polygon body. In oneembodiment the Mylar motor can be used in an arrangement for onedimensional scanning while a V-shaped taut band element (describedabove) can be used for two dimensional scanning also as discussed inmore detail below.

[0054] The preferred laser 18 is a semiconductor laser is mounted byconventional through-hole techniques on the PCB. The photodiode ispreferably an SMD (“surface mounted device”) device as is the AC coilfor the Mylar leaf spring motor. This eliminates the need for standoffsand hand-soldering or sockets, as are used on prior art scanners.Typically, the laser will be a standard packaged edge-emitting laser.For minimum cost, the laser focusing is not adjustable, and the laser issimply installed with its mounting flange in contact with a shouldermolded as part of the molded member. This will position the laseraccurately enough with respect to the molded focusing lens 20 to provideadequate performance within an inexpensive scanner. The fact that thefocusing lens is molded as part of the same component as the shoulder 54minimizes tolerance build-ups that could otherwise cause improperfocusing.

[0055] As shown in FIG. 2 of the drawing, the laser 208 hasdownwardly-extending electrical leads 227 which are simply installeddirectly into the PCB 226. This eliminates hand-soldering, but solderingcould be used if desired.

[0056] The collector optic 222 may be coated with a reflective coatingso that light impinging upon it will be reflected downwardly toward thephotodetector 40. This coating may also cover that part 62 of the moldedmember that serves as a housing for the photodiode. This will render theoptics assembly opaque in that area to prevent any light from reachingthe photodiode except via the aperture 36 and the filter 38.

[0057] This reflective coating may also serve another function.Typically, the coating will be a thin film of metal such as gold,aluminum or chrome. These films are electrically conductive. AAccordingly, the film also acts as an electromagnetic interferenceshield for the photodiode 40. The use of a surface coating to protectthe photodiode enables the usual EMI shield to be dispensed with,thereby eliminating both the cost of a separate shield and the labor tohave it installed within the assembly.

[0058] The coating is electrically grounded by extending a projection 66of the molded member into a small socket 68 in the PCB. Alternatively,the projection 66 could be press-fitted into a plated through-hole inthe board.

[0059] The housing portion 62 of the molded member 52 not only acts tohold the optical filter 38 in place on top of the photodiode 40, butalso entirely surrounds the photodiode, thereby preventing stray lightfrom reaching it. The aperture 36 in the housing may be small to limitthe f field of view of the detector, maximizing ambient light immunity.The aperture needs to be accurately located with respect to thecollector mirror 26, to allow the use of a minimum-sized field of view.Accurate relative positions of the aperture and the collector mirror areeasily achieved since they are molded as a single part.

[0060] The use of an unbalanced mirror, i.e. one in which nocounterweights are provided in the mirror assembly, is particularlysuitable in implementation in which the mirror is driven at a speed ofgreater than 100 scans per second. With an unbalanced mirror, since theattachment points of the mirror to the flexible springs is not thecenter of mass of the mirror assembly, while the mirror is at rest,gravity will exert a relatively greater force on the side of the mirrorassembly having the greater mass, causing the mirror to “droop” on itsheavier side and pull on the flexible springs. Of course, the effect ofsuch force depends on the orientation of the scanner with respect to theforce vector of gravity. The same “drooping” effect is present when themirror is scanning at relatively low speeds, so in such applications theuse of a balanced mirror would be preferred. A balanced mirror, however,requires additional mass be added to the mirror, or mirror assembly,which is a drawback in terms of operating design weight andconsequentially the power requirements.

[0061] In the embodiment of high speed operation (i.e. at more than 100scans per second), the material composition, size, shape and thicknessof the spring may be appropriately selected to achieve the desiredresonant frequency. For example, for operation at approximately 200scans/second, the selection of a Mylar spring with a thickness of 4 milis appropriate. For operation at 400 scans/second, a stainless steelspring with a thickness of about 3 mil is preferred.

[0062] Typically, the intensity of the collected reflected light signalfrom the middle portion of the scan line is much higher than the onecollected from the of the scan line when using a conventional singlelens design. One embodiment of the present invention is to use a lensarray(s). The lens array may have more than two lenses. Each individuallens of the array collects signal from a particular portion of the scanline. The field of view (FOV) of each lens may overlap. The size of eachlens and orientation may be optimized in such a way to provide desiredsignal uniformity along the scan line.

[0063] As illustrated in FIG. 3, each lens of the array may have anindividual detector which is in turn connected to an amplifier. The gainof each amplifier may be adjusted to optimize signal uniformity alongthe scan line.

[0064] If the FOV of individual lenses are not overlapping, then thesignals from those lenses may be combined together in such a way tosubtract the ambient light and improve ambient light immunity of theentire system. For example, if the FOV A does not overlap with FOV C.Assuming that the ambient light is roughly uniform across each FOV thenif the signals are subtracted, the ambient light is reduced but theuseful signal of the laser beam is not since the laser spot does notpresent simultaneously in both FOVs. Subtracting the photodiode signalcan be done in real time by reversing the signal with an appropriateelectronic circuitry. For example, the use of the combination defined bySIGNAL=|A−C|+|B−D| may reduce the ambient light contribution.

[0065] Signal uniformity as a function of the scan angle is veryimportant for reliable bar code reader performance. The amount of signalcollected by the collection optics may vary substantially with the scanangle. Typically, the signal varies as the fourth power of the cosine ofthe incident beam angle. Such signal variations limit the scannerperformance, or may require complex electronics to compensate for theeffect.

[0066] Typically the intensity of the signal from the middle portion ofthe scan line is much higher than the intensity of the signal from lightcollected from the edge. One embodiment of collector optics design canimprove the signal uniformity by equalizing the strong signal from themiddle of the scan line (on axis) to the level similar to the one fromthe edge of the scan line (off axis).

[0067] Referring to FIGS. 4 and 5, depicting a lens designs for use in acollection optics assembly, the rays from the middle of the scan lineincidents with an angle on the second surface of the lens as shown bythe “On Axis Rays”. Due to total internal reflection (TIR) the raysreflects from this surface and incident again on another portion of thesecond surface, then undergo the second TIR and reflected away from thesecond surface. Some of the rays may not undergo TIR and may passthrough the surface to the detector, as shown as the “Off Axis Rays”.However, the net effect is that the number of rays which can reach thedetector is reduced and the signal is smaller. If the rays are incidenton the surface with an angle less than the critical angle (see theFigure depicting “Off Axis Rays” from the edge of the scan line), therays may pass through the surface with no TIR and reach the detector.

[0068] In another embodiment, the present invention provides a sensorfor detecting the reflected light and for generating an electricalsignal corresponding to the symbol, the sensor including selectivelyactivatable discrete first and second portions for receiving reflectedlight from respective first and second portions of the targetcorresponding to the position of the spot beam on the target.

[0069] In one embodiment, the sensor is vertically arranged such thatthe return light from an upper portion of the target is directed to thefirst portion, and the return light from a lower portion of the targetis directed to the second portion. This embodiment is particularly suitto scanning a two-dimensional target, e.g. by a raster scanning beam.

[0070] In another embodiment, the sensor is horizontally arranged suchthat the return light from a right side of the target is directed to thefirst portion, and the return light from a left side portion of thetarget is directed to the second portion.

[0071] As a result, the strength of the collected light signal from thesignal received from the edge of the scan line is increased, while thesignal received from the middle is reduced.

[0072] A similar approach is to provide collection optics so that thelens collects less light from one particular direction (e.g., the middleof the scan line) and more form the other (e.g., the edge of the scanline).

[0073] Turning to the second lens design, shown in FIG. 6, the secondsurface of the lens has a free form surface, which in preferredembodiment may be sinusoidal as shown in the Figure.

[0074] For the rays which are in the middle of the scan line, and alongthe optical axis of the collection liens, the lens has negative powerand therefore, disperses the rays and reduces the light intensity on thedetector. For the rays which are from the ends of the scan line, and areincident on the lens with an angle, the lens has a positive power andcollects more rays and increases the light intensity on the detector.

[0075] It will be understood that each of the features described above,or two or more together, may find a useful application in other types ofscanners and bar code readers differing from the types described above.

[0076] While the invention has been illustrated and described asembodied in a scan module for an electro-optical scanner, it is notintended to be limited to the details shown, since various modificationsand structural changes may be made without departing in any way from thespirit and scope of the present invention. In particular it will berecognized that features described in relation to one embodiment can beincorporated into other embodiments as appropriate in a manner that willbe apparent to the skilled reader.

[0077] Without further analysis, the foregoing will so fully reveal thegist of the present invention that others can, by applying currentknowledge, readily adapt it for various applications without omittingfeatures that, from the standpoint of prior art, fairly constituteessential characteristics of the generic or specific aspects of thisinvention and, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims. What is claimed as new and desired to be protected byLetters Patent is set forth in the appended claims.

We claim:
 1. A scan module for use in bar code reading systems forreading indicia having portions of different light reflectivity andlocated on a target at a distance from the scan module, comprising: a)generally rectangular module including a support having a generallyplanar base, a front side, a rear side, and peripheral sides generally;b) a laser light source mounted on the support for producing a lightbeam; c) a scan mirror mounted on the support in spaced relationship tothe light source and positioned so that the light beam from the lightsource is directed by the scan mirror along a first optical path to afold assembly mounted on the support which directs the light beam alonga second optical path exterior to the scan module in the direction fromthe rear side to the front side in the direction of the target; d) adrive moving the scan mirror so that the light beam is moved in ascanning pattern substantially parallel to the planar base of thesupport and across the indicia to be read; and e) at least one sensormounted on the support for directly receiving reflected light from thetarget and converting the reflected light in to an electrical signal. 2.A module as defined in claim 1, wherein said planar base defines areference plane and the scan mirror is arranged such that the scanningbeam as it is emitted from the folded assembly defines a scanning linewhich is generally wider than to the width of the planar base over whichit is directed.
 3. A module as defined in claim 2, wherein said foldassembly includes first and second fold mirrors that direct the lightbeam along a scanning plane which is parallel to the reference plane andextends over at least a portion of the planar base.
 4. A module asdefined in claim 1, wherein said drive is operative for reciprocallyoscillating the scan mirror to sweep the light beam across the symbol atmore than 100 times per second, said drive including a holder having oneend mounted to one side of the mirror, and another portion end mountedto one end of a flexible leaf spring on which the scan mirror is mountedto the base.
 5. The module as defined in claim 1, wherein said driveincludes a flexible leaf spring on which the scan mirror is mounted. 6.A module as defined in claim 4, wherein said drive includes anenergizable electromagnetic coil drive member and a permanent magnetdrive member in operational proximity thereto for imparting a force tothe scan mirror, thereby resulting in oscillating movement of the scanmirror about an axis passing through the leaf spring, and therebycausing the light beam reflected off the scan mirror to sweep along ascanning path.
 7. A module as defined in claim 4, wherein said driveincludes: a) a generally planar, elongated flexure having one end regionconnected to the support, and opposite end region; b) an elongatedactuation arm connected to the opposite end region of the flexure andhaving opposite end portion, the actuation arm being attached to theflexure at a region between the opposite end portion of the actuationarm; c) a magnet attached to the other end portion of the actuation arm;and d) an electromagnic drive for exerting a force upon the magnet andfor moving the magnet, the actuation arm and the scan mirror to scan thelight beam across the indicium.
 8. The module as defined in claim 7,wherein the magnet and the reflector have respective mass that balanceeach other.
 9. A scan module as defined in claim 1, wherein the sensoris positioned beneath the scanning plane of the emitted light beam andabove the base of the support.
 10. A scan module for use in bar codereading systems for reading indicia having portions of different lightreflectivity and located on a target at a distance from the scan module,comprising: a) generally rectangular step shaped module including asupport, a front side, a rear side, and peripheral sides generallyorthogonal thereto, and first and second top surfaces; b) a laser lightsource mounted in the module for producing a light beam; c) a scanmirror mounted on the support in spaced relationship to the light sourceand positioned so that the light beam from the light source is directedby the scan mirror along a first optical path to a fold mirror mountedadjacent the rear side of the support which directs the light beam alonga second optical path over the first top surface and in the directionfrom the rear side to the front side in the direction of the target; d)a drive moving the scan mirror so that the light beam is moved in ascanning pattern substantially parallel to the first top surface andacross the indicia to be read; and e) at least one sensor mounted on thesupport for directly receiving reflected light from the target andconverting the reflected light in to an electrical signal.
 11. Anon-retro-reflective optical scan module comprising: a) a support; b) alight source mounted on the support, for generating and directing thelight beam along a first optical path; c) a first reflective element inthe first optical path for receiving the light beam and for re-directingthe light beam along a second optical path substantially coplanar withsaid first optical path; d) a second reflective element for receivingthe light beam transmitted along the second optical path and forre-directing the light beam along a third optical path which extendsover said second optical path relative to said support; e) a thirdreflective element for receiving the light beam transmitted along thethird optical path and for re-directing the light beam along a fourthoptical path over said second and said third optical paths relative tosaid support; and extends substantially parallel to said second opticalpath and projects the beam exteriorly of the module; and f) a sensormounted on the support for detecting the reflected light from thetarget, and for generating an electrical signal corresponding to thedetected light intensity.
 12. An optical reader for scanning a lightbeam across an optical code symbol having regions of different lightreflectivity, comprising: a light source for generating a light beam;scanning optics with at least one moving optical element for scanningthe light beam in a scanning line across the symbol; light collectionoptics for collecting the incoming reflected light and for directing thelight to a sensor assembly; the sensor assembly including more than oneindividual light detection elements, each element having a field of viewover a different portion of the scan line and each having an outputcapable of providing an output signal representative of light impingingsuch element, the output of each detection element being coupled to arespective amplifier for amplifying the output signal of a respectiveelement.
 13. An apparatus for reading bar code symbols having parts ofdifferent light reflectivity by a scanning beam which forms a scan linethrough the bar code symbol comprising: focusing optics for collectinglight reflected off at least a portion of the bar code symbol includinga first surface for receiving the incoming light, and a second surfacehaving a configuration such that rays collected from the middle of thescan line are attenuated relative to the rays collected form the ends ofthe scan line; a photosensor positioned so as to receive light collectedby said focusing optics and transmitted through said second surface, andgenerating an electrical signal indicator of the detected lightintensity;
 14. An apparatus for reading bar code symbol having parts ofdifferent light reflectivity comprising: focusing optics for collectinglight reflected off at least a portion of the bar code symbol having asurface having a cross-section of a cosine function over one cycle; anda photosensor positioned so as to receive light collected by saidfocusing optics, and generating an electrical signal indicator of thedetected light intensity;
 15. An optical scanner for reading an opticalcode Symbol having a pattern of different light reflectivity,comprising: light source for producing a light beam; and a scanningassembly for receiving the light beam and producing a moving spot beamscanning pattern on the target; and a sensor for detecting the reflectedlight and for generating an electrical signal corresponding to thesymbol, said sensor including selectively activatable discrete first andsecond portions for receiving reflected light form respective first andsecond portion of the target corresponding to the position of the spotbeam on the target.
 16. A module as defined in claim 15, wherein saidsensor is vertically arranged such that the return light from an upperportion of the target is directed to said first portion, and the returnlight from a lower portion of the target is directed to said secondportion.
 17. A module as defined in claim 15, wherein said sensor ishorizontally arranged such that the return light from an right side ofthe target is directed to said first portion, and the return light froma left side portion of the target is directed to said second portion.